The present invention relates to a data recording/reproducing apparatus for recording data onto, or reproducing data from, a recording medium. More particularly, the invention relates to a method of highly precisely recording and reproducing recording marks relying upon thermal recording and to an apparatus therefor.
In a conventional recording system as disclosed in Japanese Patent Laid-Open No. 22223/1991, a sequence of recording codes of recording marks are converted into pulses to form a sequence of pulses corresponding to the length of the sequence of recording codes. The length and amplitude of the sequence of pulses are controlled depending upon the length of an opposite phase of the sequence of recording codes located just before the sequence of recording codes. The sequence of pulses is divided into three parts, and the widths of the pulses are changed to execute the recording.
In the above-mentioned prior art, however, no attention has been given to the fact that the recording sensitivity of the recording medium changes due to a change in the thickness of the recording medium or a change in the ambient temperature, and that a relative recording sensitivity changes due to a change in the position of a light spot of the recording/reproducing apparatus. Therefore, the recording mark is not highly precisely controlled causing the recording capacity to decrease. The object of the present invention is to minimize the change of the recording mark caused by a change in the recording sensitivity and to control the recording mark highly precisely.
In order to improve matching between the recording medium and the recording apparatus according to the present invention, trial writing is effected in advance into a predetermined position of the recording medium. Optimum light powers for recording during the recording and optimum servo conditions are found from reproduction signals obtained by the trial writing and, then, the recording of normal data is started.
The trial writing data and a sequence of input data bits of normal data are converted into a sequence of codes that correspond to a modulation system of the recording apparatus. It is desired to form a sequence of data to record the sequence of codes into the recording medium, and drive a laser beam source of to form a recording area in the recording medium thereby to effect correct recording. This makes it possible to handle the trial writing data and normal data using a common circuit.
When data are to be recorded into, and erased from, the recording medium using two or more energy levels, it is desired that the light power is optimized during the recording for each of the energy levels. This constitution makes it possible to further improve matching between the recording/reproducing apparatus and the recording medium, so that the data can be reliably recorded and erased.
The present invention compensates for a change in the recording sensitivity that is caused by a change in the thickness of each of the recording medium, by a change in the ambient temperature and by a change in the characteristics of the recording apparatus. For this purpose, a predetermined trial writing pattern having a severe recording condition is written into the recording medium prior to recording normal data. In order to detect an optimum light power for recording, the recording operation is carried out while changing the light intensity or the energy of the waveform for recording, and the recorded data are reproduced and are evaluated to determine an optimum light power for recording. Moreover, the condition for controlling the position of light spot, such as focusing, tracking, etc., changes accompanying a change in the characteristics of the recording apparatus. Therefore, the trial writing pattern is recorded while changing the condition for controlling the position of the light spot, and the trial writing pattern is reproduced to determine optimum control conditions. In practice, first, an optimum light power for recording is roughly set and, then, the condition for controlling the position of the light spot is set. As the condition for controlling the position of the light spot changes, the optimum light power for recording changes, too. Therefore, the light power for recording is set again in order to eliminate erroneous operation in recording the data caused by a change in the recording sensitivity and to effect the recording and reproduction maintaining improved reliability.
When the data recorded using other apparatus are to be reproduced, it is desired to prevent as much erroneous operation as possible during the reproduction caused by variance in the characteristics between the apparatuses. For this purpose, trial reading is effected to reproduce a predetermined pattern prior to reproducing normal data, and the reproducing condition is set based upon the result of trial reading in order to improve matching between the recording marks and the reproducing apparatus.
In this specification, pits formed in the optical recording medium by the irradiation of light, magnetic recording domain, change in the phase and change in the color are all referred to as recording marks.
In the optical recording, the optical recording medium is irradiated with a laser spot of a diameter of about 1 μm to locally heat that part in order to form a recording mark of a binary code. In the case of the magneto-optical recording, however, the recording is usually effected by being irradiated with a laser spot and by the application of an external magnetic field in combination.
The system for recording data for the binary coded data includes an inter-mark recording system and a mark length recording system. As for the data “010010”, for instance, the former system gives a mark relying upon the optical spot onto a central portion of the data “1” and the data “0” is placed between the two marks corresponding to two “1s”. In the latter system, the mark is raised relying upon the light spot at the central position upon the arrival of the first “1”, the mark is lowered at the center when the next “1” has arrived, and the mark is raised when “1” after the next “1” has arrived. That is, the data “0” is placed between the two edges between the raising of the mark and the lowering of the mark.
As a record control method which easily accomplishes high precision by utilizing a mark length recording system, the present inventors have previously proposed a method of controlling record into a magneto-optical disk by controlling the output of laser beam by superposing a plurality of kinds of pulses having different pulse widths and pulse levels (Japanese Patent Application No. 238276/1992).
FIG. 19 schematically illustrates this method, wherein FIG. 19a is a diagram illustrating laser outputs for making a record into a magneto-optical disk, FIG. 19b is a diagram illustrating a temperature distribution of the magneto-optical disk heated upon the irradiation with a laser beam, and FIG. 19c is a diagram showing recording marks recorded into the magneto-optical disk.
A minimum level in the laser beam output is a light power Pr during the reproduction. The power level Pa is such that the magneto-optical recording medium is heated to some extent even during the rest period of a sequence of recording codes and that the temperature distribution is maintained constant at a moment of the rise of the recording pulse for writing the next recording mark. The recording pulses consist of a relatively broad head pulse 40 and relatively narrow one or a plurality of succeeding pluses 41. The head pulse 40 has a recording power level Pw1 and the succeeding pulses 41 have a recording power level Pw2.
The temperature is raised by the head pulse 40 in the laser beam output waveform shown in FIG. 19a, and the temperature is maintained nearly constant by the succeeding pulses 41. Therefore, the temperature distribution corresponding to the recording pulse irradiation period and the rest period can be controlled to be constant, and the temperature distribution is imparted to the disk medium as shown in FIG. 19b. Thus, by setting the temperature level of the magneto-optical recording medium to be constant, the width and length of the recording mark are controlled to be within a predetermined precision shown in FIG. 19c. 
According to the above-mentioned recording method, the temperature distribution is maintained nearly constant on the magneto-optical recording medium during the irradiation with recording pulses, and the high-density recording is accomplished maintaining high precision.
Even by the above-mentioned recording method, however, a change in the power supply which feeds electric power to the recording apparatus results in a change in the recording power or in the width of the recording pulse, which is a cause of change in the recording sensitivity for the recording medium, making it difficult to utilize the above-mentioned advantage to a sufficient degree.
In the inter-mark recording system, even a slight change in the width of the recording pulse or in the power level simply results in a change in the size of the mark in the form of a concentric circle without almost causing the center position of the recording mark to be deviated, and no problem arises. In the case of the mark length recording system, on the other hand, the mark length for recording the data undergoes a change, which is much of a problem.
The object of the present invention is to suppress as much as possible the change in the recording mark caused by a change in the power supply in the optical recording apparatus, and to control the recording mark maintaining high precision.
Another object of the present invention is to increase reliability of the optical recording apparatus in order to increase the storage capacity and the transfer rate of the data.
The above-mentioned object is accomplished by detecting the power supply voltage applied to the optical recording apparatus, and by changing the light source drive pulse, i.e., by changing the power level of the light pulse maintaining a predetermined relationship depending upon the power supply voltage that is detected. It is desired that the power supply voltage is detected at least prior to starting the recording operation.
The above-mentioned recording method can be adapted to the mark length recording system which is constituted by a relatively broad head pulse that rises in synchronism with the rise of a recording code period in the sequence of recording codes and relatively narrow one or a plurality of succeeding pulses of which the final falling portion is in synchronism with the fall of the recording code period.
The power level of the light pulse is controlled by so controlling the power level of the succeeding pulses that the ratio of the power level of the succeeding pulses to the power level of the head pulse assumes a value that has been determined in advance depending upon the power supply voltage.
When the data are to be recorded by the ZCAV (zoned constant angular velocity) system in which a reference clock is changed for each of the zones to maintain the recording density nearly constant in the inner and outer circumferences, it is desired that the ratio of the power level of the succeeding pulses to the power level of the head pulse determined in advance depending upon the power supply voltage is changed depending upon the recording position in the radial direction of the optical recording medium.
According to the present invention, the optical recording apparatus comprises a source of laser beam, an optical system for converging the light beam from the source of laser beam onto an optical recording medium, a recording waveform forming means for forming a sequence of recording pulses including a relatively broad rectangular head pulse that rises in synchronism with the rise of the recording code period based upon the recording code sequence data and relatively narrow one or a plurality of succeeding rectangular pulses, the final falling portion of which being in synchronism with the falling of the recording code period, a laser drive means for driving the source of laser beam using the sequence of recording pulses formed by the recording waveform forming means, a power supply voltage detecting means, and a means for compensating a change in the power supply voltage to compensate, depending upon the power supply voltage detected by the power supply voltage detecting means, the power level of a light pulse generated from the source of laser beam in response to the rectangular head pulse and the succeeding rectangular pulses, whereby a change in the power supply voltage is compensated to form recording marks maintaining high precision.
Means for compensating a change in the power source may include means for controlling the power level of light pulses generated from the source of laser beam in response to the succeeding rectangular pulses, so that the ratio of the power level of light pulses generated from the source of laser beam in response to the succeeding rectangular pulses to the power level of a light pulse generated from the source of laser beam in response to the rectangular head pulse, assumes a value that has been determined in advance depending upon the power supply voltage.
When the optical recording is the magneto-optical recording, the optical recording apparatus includes an external magnetic field application means, and the recording is effected by being irradiated with a light spot and by the application of a magnetic field from the external unit in combination.
The present invention can be applied not only to a recording system which records the data using light pulses of a plurality of kinds having different pulse widths and power levels but also to a recording system which effects the recording using light pulses, as well as to recording systems other than the mark length recording system.
A change in the power supply voltage during the optical recording results in a change in the drive current characteristics and drive frequency characteristics of the laser driver. In particular, a high drivability is required as the recording frequency increases. When the supply voltage drops, therefore, the rising time of the recording waveform is delayed. As the recording frequency increases, the recording pulse width becomes narrow, the total recording power decreases, and it is no longer possible to correctly record the data. Furthermore, the recording power (crest value) tends to decrease. When the applied voltage is high, on the other hand, the recording power becomes too great and the data are not correctly recorded.
As shown in FIG. 14, for instance, when the voltage of the power supply applied to the optical recording apparatus is as represented by a solid line 320 which is that of the waveform of practical laser drive pulses of a rated power supply voltage, the waveform of the laser drive pulses changes as represented by a broken line 330 when the power supply voltage is lowered. The power of light pulse generated from the source of laser beam changes like the waveform of the laser drive pulses. The effective energy that contributes to the optical recording is the energy before the power reaches the highest value; i.e., the energy in the falling portion after the power has reached the highest point does not much contribute to the recording.
The effect of a change in the power supply voltage, in the case of the sequence of recording pulses of FIG. 19a, appears conspicuously for the succeeding pulses 41 which determine the rear end position of the recording mark 23. When the power of the succeeding pulses 41 changes, the length of the recording mark changes, which results in the occurrence of erroneous recording. When the recording method called ZCAV (zoned constant angular velocity) is employed in which the reference clock is changed for each of the zones so that the recording density is nearly constant in the inner and outer circumferences in order to increase the recording capacity, the above-mentioned effect becomes more serious since the recording frequency becomes higher toward the outer circumferential portion of the recording medium than in the inner circumferential portion.
As described above, a change in the power supply voltage appears as a change in the width of the pulse for driving the source of light and as a change in the power level. According to the present invention, the power level only is not simply rendered to become constant but also a change in the pulse width is reflected in controlling the power level, so that the power that contributes to the recording becomes constant. The amount of change in the recording power due to a change in the power supply that supplies power to the recording apparatus and the amount of change in the average recording power due to a change in the recording pulse width, are measured in advance, and the setpoint value of the recording power is changed depending upon the change in the power supply voltage, so that the recording medium is irradiated with nearly the same recording power irrespective of a change in the power supply voltage.
In practice, the recording power and a decrease in the irradiation power caused by a change in the recording pulse width are measured for each of the apparatuses, and a power level of light pulses that offsets the change is found. The power source voltage and the setpoint power level of light pulses are stored in the recording apparatus, an optimum power level of drive pulses is set to the recording apparatus from a relationship between the power supply voltage and the preset power level of light pulses based upon the voltage measured by a power supply voltage measuring device in the recording apparatus, and the recording power is irradiated with nearly the same recording power at all times irrespective of a change in the power supply voltage. This makes it possible to improve matching between the recording medium and the recording apparatus despite a change in the power supply voltage, and erroneous operation can be avoided.
Even when the power supply voltage is raised, the setpoint power level of pulses for driving the light source is lowered in the recording apparatus, so that the recording medium is irradiated with an optical recording power avoiding erroneous operation.
According to the present invention, the recording marks can be recorded highly precisely making it possible to improve reliability of the optical recording apparatus. Moreover, owing to their high recording precision, the recording marks can be densely recorded to increase the recording density and the rate for transferring the data.